The present invention relates to substrates for the epidermal growth factor receptor kinase, polynucleotide encoding those substrates, and methods for using the substrates.
The cellular machinery involved in mitogenesis is complex, and not fully understood. In general, receptors present on the cell surface bind growth factors, resulting in an activated receptor. In particular, the receptors of interest are endowed with intrinsic tyrosine kinase activity, and are known as tyrosine kinase receptors or TKRs. The activated receptors, in turn, phosphorylate intracellular substrates. These phosphorylated substrates are responsible for a series of events that leads to cell division. This process is generally referred to as "mitogenic signal transduction." The molecular machinery involved in this process is considered to be the "mitogenic signaling pathway."
Growth factors and hormones exert pleiotropic effects on cellular functions, including mitogenic stimulation and modulation of differentiation and metabolism (Ullrich, et al. Cell 61: 203-212 (1990); Aaronson, S. A. Science 254: 1146-1153 (1991)). In many cases, these actions are mediated by the interaction of growth factors with cell surface tyrosine kinase receptors (TKRs), which results in enhanced receptor catalytic activity and tyrosine phosphorylation of intracellular substrates (Ullrich, et al., supra, Aaronson, supra). Knowledge of the nature of these second messenger systems is still scanty, although some molecules which associate and/or are tyrosine phosphorylated by TKRs have been identified. These include the .gamma. isozyme of phospholipase C (PLC-.gamma.) (Margolis, et al. Cell 57:1101-1107 (1989), Meisenhelder, et al. Cell 57:1109-1122 (1989) and Wahl, et al. Mol. Cell. Biol. 9: 2934-2943 (1989)); the p21ras GTPase activating protein (GAP) (Molloy, et al. Nature 342: 711-714 (1989), Kaplan, et al. Cell 61: 125-133 (1990), and Kazlauskas, et al. Science 247: 1578-1581 (1990)); the raf serine-threonine kinase (Morrison, et al. Proc. Natl. Acad. Sci. USA 85: 8855-8859 (1988), and Morrison, et al. Cell 58: 649-657 (1989)); the p85 subunit of the phosphatidylinositol 3-kinase (PtdIns-3K); (Coughlin, et al. Science 243: 1191-1194 (1989), Kazlauskas, et al. Cell 58: 1121-1133 (1989), Varticovski, et al. Nature 342: 699-702 (1989), Ruderman, et al. Proc. Natl. Acad. Sci. USA 87: 1411-1415 (1990), Escobedo, et al. Cell 65: 75-82 (1991), Skolnik, et al. Cell 65: 83-90 (1991), Otsu, et al. Cell 65: 91-104 (1991)) and some cytoplasmic tyrosine kinases (Gould, et al. Mol. Cell. Biol. 8: 3345-3356 (1988); Kypta, et al. Cell 62: 481-492 (1990)). These signaling molecules are thought to mediate at least in part the mitogenic effects of TKRs (Ullrich, et al. supra; Aaronson, supra).
However, the Epidermal growth factor (EGF) receptor (EGFR) does not appear to efficiently interact with known second messenger systems (Fazioli, et al. Mol. Cell. Biol. 11: 2040-2048 (1991); Segatto, et al. Mol. Cell. Biol. 11: 3191-3202 (1991)). Thus, there is a need to ascertain the mechanism by which the EGFR functions in mitogenesis, and a particular need to identify and characterize the substrate (if any) of the EGFR.
Errors which occur in the mitogenic signaling pathway, such as alterations in one or more elements of that pathway, are implicated in malignant transformation and cancer. It is believed that in at least some malignancies, interference with such abnormal mitogenic signal transduction could cause the cells to revert to normal phenotype.
In addition, reagents useful in identifying molecular components of the mitogenic signaling pathway find utility as tumor markers for therapeutic, diagnostic, and prognostic purposes. Furthermore, identification of how such components differ from normal components in malignant tissue would be of significant value in understanding and treating such malignancies. Alterations of the EGFR mitogenic signal transduction have been described in several human tumors. Accordingly, substrates of EGFR are of particular interest.
Finally, there is a need for reagents for determining the tyrosine kinase activity of particular samples of biological origin.
It is therefore an object of the present invention to provide reagents and methods useful in identifying components of the mitogenic signal transduction pathway, for determining tyrosine kinase activity of samples, and for determining how particular components of the pathway in abnormal tissue differ from normal components. In particular, it is an object of the invention to provide such reagents and methods that relate to the substrate of the EGFR.